An oil lash adjuster makes use both of elastic material and oil pressure to achieve zero lash operation in a valve system. It has the advantage of being quiet in operation and maintenance free, and is hence employed in a variety of 4-cycle engines.
The lash adjuster disclosed in Japanese Pat. No. 54-142179 (1979) supports one end of a rocker arm which opens and closes the valve of a 4-cycle engine. A valve cam is positioned on the upper end of the rocker arm, and this enables zero lash operation of the valve system.
The lash adjuster according to this patent is composed of a cylindrical plunger body with a closed bottom, having a plunger sliding within it so as to create a high pressure chamber between the plunger and bottom of the plunger body. The elastic material of the plunger is retained within the plunger body by means of a snap ring which fits within an annular groove in the upper end of the interior surface of the plunger body, and prevents the plunger from being withdrawn upwardly.
The lash adjuster according to the above-mentioned patent will be described in more detail with reference to the drawings. It has the disadvantage that, while sufficient force is needed in order to secure the lower edge of the diaphragm to the plunger body, excessive force must be avoided because the diaphragm used is made of soft material between the plunger body and a metal retainer which is pressure fitted.
In a further embodiment of the prior art structure, an annular groove is formed in the upper portion of the outer surface of the plunger body, and the diaphragm is provided with an annular projection, also of soft material, which fits into that groove. Because of the softness of this projection, the structure is not securely attached together.